The aim of this prospective in vivo randomized clinical trial to evaluate influence of combination of calcium Hydroxide (CALCIPAST Paste, Poland) and chlorhexidine Gel 2% (Gluco-Chex 2%, Cerkamed, Poland) in comparison to calcium hydroxide paste (CALCIPAST Paste, Poland) as Intracanal Medication on post operative pain (incidence, degree, duration) and reduction of bacterial endotoxins (quantitative) after endodontic treatment in single rooted necrotic teeth.

According to the inclusion criteria the patients enrolled in the study and allocated randomly into three groups either combination of calcium hydroxide paste intracanal medication with 2% chlorhexidine gel. (group A) or calcium hydroxide paste intracanal medication only (group B) or mechanical preparation without intracanal medications (group C) the endodontic treatment is done at two visits.

The samples of endotoxin divided into three groups: after access (S1), after mechanical instrumentations (S2), after removal intracanal medication (S3), all samples taken by a sterile paper points introduced in the root canal for the working length for 60 seconds.

firstly the patient's medical and dental history is taken. the patients assign on informed consent. and then anaesthetized and access cavity performed and root canal preparation is done by Revo-s system then irrigation and intracanal medication placement inside to canal. the patient's record the post operative pain in sheet with NRS after 4, 24, 48 hours and 2 weeks after first visit. the operator will recall the patient to check the records

second visit After 2 weeks from application of ICM, rubber dam will be applied then removal of the temporary dressing, then a sterile paper point (S3) will be introduced into the canals after irrigation and removal of the remnants of the intracanal medicament with the saline solution.

• Removal of the paper sample to determine the endotoxin concentration.
• The canals will be obturated by single cone technique using gutta percha point tapered 0.4% (Gutta percha point, Revo-S MicroMega CO., LTD, France) corresponding to the final apical size of the file and the root canal sealer will be resin sealer (Adseal, META BIOMED CO., LTD, Korea).
• Pain will be assessed by numerical pain rating scale (NRS) after 14 days from the first visit (at the day of the Obturation) before the beginning of Obturation.

Medical and dental history: diagnostic charts will be collected in a case report from by the investigators and confirmed for eligibility with the assistant supervisor.

Radiographic examination: preoperative radiographs will be taken to examine the tooth structure, caries detection, periapical status.

Clinical examination: intraoral examination include visual examination for caries, restorations, swelling, fistula, mobility, percussion were done.

Diagnostic criteria for necrotic tooth:

1. The patient marks moderate to severe pain on the numerical rating scale (NRS)a horizontal line of 11 marks and 10 intervals each takes number form 0 - 10 0 reading represents "no pain", 1- 3 readings represent "mild pain", 4- 6 readings represent "moderate pain", 7- 10 readings represent "severe pain".

   (recording baseline degree of pain preoperatively before initiating the endodontic treatment ) All step will done by operator.

   The measurement time will be at 4 hours, 24 hours, and 48 hours and after 14 days. (Day of Obturation)

2. The patient not responding to electric pulp tester at higher level than the contralateral tooth or the adjacent tooth if the contralateral one is missing.

3. Preoperative periapical x- ray film is done to detect any periapical changes.

Intervention:

Forty five patients will include were allocated by random or by chance to receive several clinical interventions and one of these interventions was control (Group A) where the patients did not receive any intracanal medication, (Group B) where the patients receive intracanal medication calcium hydroxide (CALCIPAST Paste, (Poland) and chlorhexidine 2 % gel. (Gluco-Chex 2%, Cerkamed, Poland), (Group C) calcium hydroxide paste only CALCIPAST Paste (Poland).

Procedure steps:

At the 1st appointment.

• Each patient will be given a numerical pain rating scale chart in order to rate his /her presenting pain as preoperative pain
• Anesthesia will be done with Carpule 3M™ ESPE™ Ubistesin™ Articaine HCI 4% & Adrenaline 1:100,000 3M Australia the tooth with decayed using a standard dental aspirating syringe.
• After diagnosis disinfecting the tooth surface by 30% H2O2 (Perfect Medical, Egypt) followed by 2.5% NaOCl inactivated with sodium thiosulfate (El Nasr CO. for pharmaceuticals and chemicals).
• Access cavity will do under rubber dam isolation and with Sterile burs for access cavity preparation with distilled water as a coolant and flaring will done by endo-z bur.
• If successful anesthesia occurs, working length will be determined with an apex locator (Root ZX, J.Morita, Irvine, California, USA.) then confirmed with intraoral periapical radiograph (Kodac Dental film, speed D, size 2, Carestream Health, Rochester, NY, USA) to confirm the length to be 0.5-1 mm shorter than radiographic apex.
• The first sample of endotoxin (S1) is taken by a sterile paper points after access cavity preparation and introduced in the root canal for the working length for 60 seconds.
• The sample is then placed in a pyrogenic free plastic tube and frozen to negative 200c for endotoxin determination by LAL test.
• Canal instrumentation will be done using NiTi rotary files system (Revo-S MicroMega, France) in an endodontic motor (X-Smart, Dentsply Maillefer, USA.) according to the manufacturer instructions to ensure adequate space for placement of the intracanal medicaments and proper removal of bacteria and debris, till size AS 35 file. The rotary files will be introduced inside the canal with EDTA gel (MD-Chelcream, META BIOMED CO., LTD, Korea) as lubricant.
• The irrigant solution will be NaOCl with concentration 2.5% for its tissue dissolving properties between each file and will be delivered by disposable plastic syringe.
• Another sample (S2) will be taken after the cleaning and shaping and before placing the intracanal medications by sterile paper point for endotoxin determination.
• The first group will be subjected to combined therapy of both calcium hydroxide intracanal medication CALCIPAST Paste (Poland), with 2% chlorhexidine gel intracanal medication (Gluco-Chex 2%, Cerkamed, Poland) after the cleaning and shaping for 2 weeks period.
• The second group will be subjected to calcium hydroxide intracanal medication alone for 2 weeks period after the cleaning and shaping. Calcium hydroxide will be in form of ready-made paste in a measured special syringe CALCIPAST (Poland).
• The third group will receive plain cotton with temporary filling without any intracanal medication.
• Placement of the intracanal medications by lentuolo spiral by low speed hand piece and condensed with paper points.
• Temporary filling is done by glass ionmer filling to ensure proper sealing with no leakage of any oral fluids inside the root canal, which may disturb the action of the intracanal medication.
• Pain will be assessed by numerical pain rating scale (NRS) will be given to each patient to complete a t home at the specified times at 4, 24, 48 hours after the first visit.

At the 2nd appointment:

• After 2 weeks from application of ICM, rubber dam will be applied then removal of the temporary dressing by following the previous infection control protocol, then a sterile paper point (S3) will be introduced into the canals after irrigation and removal of the remnants of the intracanal medicament with the saline solution.
• Removal of the paper sample to determine the endotoxin concentration.
• The canals will be obturated by single cone technique using gutta percha point tapered 0.4% (Gutta percha point, Revo-S MicroMega CO., LTD, France) corresponding to the final apical size of the file and the root canal sealer will be resin sealer (Adseal, META BIOMED CO., LTD, Korea).
• Pain will be assessed by numerical pain rating scale (NRS) after 14 days from the first visit (at the day of the Obturation) before the beginning of Obturation.

Inclusion Criteria:

• Patients in Good Health(American Society Of Anaesthesiology Class II or higher).
• Adult patients from both genders older than 18-50 years old suffering from chronic periapical periodontitis with necrotic pulp.
• single rooted teeth (maxillary and mandibular).
• Patients who can understand numerical rating scale (NRS)
• Patients able to sign informed consent

Exclusion Criteria:

• Patients with Vital tooth.
• Patients having active pain in more than one tooth.
• Patients who had taken analgesics in 12 hours preceding the preparation.
• Any type of teeth with multi roots.
• Pulp hyperemia or any other conditions other than pulp necrosis like pulpitis or previously accessed teeth with temporary fillings and patients suffering from chronic disease (systemic diseases).
• Pregnant or mentally retarded patients.